KR20220095028A - White Light Emitting Device and Light Emitting Display Device Using the Same - Google Patents

Abstract

The present invention relates to a white light emitting element and a light emitting display device including the same. The white light emitting element comprises: a first electrode and a second electrode facing each other on a substrate; a first stack emitting first light between the first electrode and the second electrode; and a second stack having first to third light emitting layers stacked thereon. Therefore, the white light emitting element can increase efficiency without a color change.

Description

White Light Emitting Device and Light Emitting Display Device Using the Same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly, to a white light emitting device and a light emitting display device including the same, in which a color difference between regions is prevented and a difference in color characteristics between a low gray scale and a high gray scale is resolved through structural change.

Recently, a self-luminous display device is being considered as a competitive application in order to make the device compact and display vivid colors without requiring a separate light source. The self-light emitting display device may be classified into an organic light emitting display device and an inorganic light emitting display device according to an internal light emitting material.

On the other hand, in a self-luminous display device, a plurality of sub-pixels are provided, and a light-emitting element is provided in each sub-pixel without a separate light source to emit light.

In addition, the display device has high resolution and high integration, does not require a metal micro mask, and a tandem device that commonly comprises an organic layer and a light emitting layer is highlighted in terms of fairness, and research is being conducted on it.

The light emitting display device of the present invention requires diversity of color expression and high efficiency, and requires a plurality of light emitting layers in a stack structure.

However, there is a difference in efficiency, etc. for each light emitting layer of different colors. In addition, when the plurality of light emitting layers are disposed, different color trends may be exhibited when driving at low current density and high current density, which is also observed as a color abnormality.

The white light emitting device and the light emitting display device including the same according to the present invention are intended to prevent a color difference for each region and resolve a difference in color characteristics between a low grayscale and a high grayscale through structural change.

A light emitting display device according to an embodiment of the present invention includes: a first stack for emitting a first light on a substrate, a first electrode and a second electrode facing each other, and between the first electrode and the second electrode; a second stack including the first stack and first to third light-emitting layers stacked with the first charge generating layer interposed therebetween, wherein the first to third light-emitting layers gradually increase as the distance from the first stack increases The light of a short wavelength may be emitted, and the thickness may be thin while going to the second light-emitting layer, the first light-emitting layer, and the third light-emitting layer.

Further, in a light emitting display device according to another embodiment of the present invention, a substrate having a plurality of sub-pixels, a first electrode provided in each sub-pixel on the substrate, and the plurality of sub-pixels facing the first electrode a second electrode provided across the pixels, between the first electrode and the second electrode, across the plurality of sub-pixels, a first stack emitting a first light, the first stack, and a charge generation layer; and a second stack having first to third light-emitting layers stacked therebetween, wherein the first to third light-emitting layers gradually emit light of a shorter wavelength as the distance from the first stack increases, the second light-emitting layer; The thickness of the first light emitting layer and the third light emitting layer may be thin.

The white light emitting device and the light emitting display device including the same according to the present invention have the following effects.

First, it is possible to increase the diversity of color expression by providing different red light emitting layers, yellow green light emitting layers and green light emitting layers in the phosphorescent light emitting stack. can be raised

Second, by making the thickness of the green light emitting layer the thinnest among the light emitting layers of different colors stacked on each other in the phosphorescent light emitting stack, the thickness of the green light emitting layer is lowered from the total thickness of the phosphorescent light emitting layer in the phosphorescent light emitting stack to reduce the sensitivity to color abnormalities caused by the green light emitting layer for each area. have. Accordingly, it is possible to prevent a color abnormality from appearing in the edge area within the display area.

Third, compared to the yellow-green light-emitting layer, the thickness ratio of the red light-emitting layer and the green light-emitting layer is set to a constant ratio, and the color coordinate fluctuations during low-current driving and high-current driving are similar in the edge area and the center area within the display area of the substrate to drive low current density. It can prevent color abnormality.

1 is a cross-sectional view showing a white light emitting device according to a first embodiment of the present invention.
2 is a cross-sectional view illustrating a white light emitting device according to a second embodiment of the present invention.
3 is a view showing a second stack of a white light emitting device of the present invention.
4A to 4D are graphs showing the relationship between current density and CIEy color coordinates of Experimental Examples 1 to 4;
5A and 5B are graphs showing the relationship between current density and CIEy color coordinates of Experimental Examples 4 and 5;
6 is a plan view illustrating a light emitting display device of the present invention.
7 is a view showing a change in the thickness of the third light emitting layer on the line I to I' of FIG. 6 .
8 is a cross-sectional view illustrating a light emitting display device of the present invention in connection with a lower driver.
9 is a circuit diagram of a sub-pixel according to an example of a light emitting display device according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Like reference numerals refer to substantially identical elements throughout. In the following description, when it is determined that a detailed description of a technology or configuration related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, the component names used in the following description are selected in consideration of the ease of writing the specification, and may be different from the part names of the actual product.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining various embodiments of the present invention are exemplary, and thus the present invention is not limited to the matters shown in the drawings. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components included in various embodiments of the present invention, it is interpreted as including an error range even if there is no separate explicit description.

In describing various embodiments of the present invention, in the case of describing the positional relationship, for example, two When the positional relationship of parts is described, one or more other parts may be positioned between the two parts unless 'directly' or 'directly' is used.

In describing various embodiments of the present invention, in the case of describing a temporal relationship, for example, a temporal precedence relationship such as 'after', 'next to', 'after', 'before', etc. When is described, a case that is not continuous may be included unless 'directly' or 'directly' is used.

In describing various embodiments of the present invention, 'first ~', 'second ~', etc. may be used to describe various components, but these terms are only used to distinguish between the same and similar components. to be. Accordingly, in the present specification, elements modified by 'first to' may be the same as elements modified by 'second to' within the technical spirit of the present invention, unless otherwise specified.

Each of the features in the various embodiments of the present invention may be partially or wholly combined or combined with each other, technically various interlocking and actuating are possible, and each of the various embodiments may be operable independently of each other or together in a related relationship. It may be feasible.

In the present specification, 'doped' refers to a material occupying most of the weight ratio of a layer, and different physical properties from the material occupying the majority of the weight ratio (different physical properties are, for example, N-type and P-type, organic material and It means that the material having inorganic substances) is added in an amount of less than 30% by weight. In other words, the 'doped' layer means a layer capable of distinguishing a host material and a dopant material of a certain layer in consideration of the specific gravity of the layer. And 'undoped' refers to all cases other than the case corresponding to 'doped'. For example, when a layer is composed of a single material or a mixture of materials having the same properties as each other, the layer is included in the 'undoped' layer. For example, if at least one of the materials constituting a layer is P-type and all materials constituting the layer are not N-type, the layer is included in the 'undoped' layer. For example, if at least one of the materials constituting a layer is an organic material and all materials constituting the layer are not inorganic materials, the layer is included in the 'undoped' layer. For example, when materials constituting a certain layer are all organic materials, and at least one of the materials constituting the layer is N-type and at least one other is P-type, an N-type material If this weight ratio is less than 30%, or if the P-type material is less than 30% by weight, it is included in the 'doped' layer.

Meanwhile, in this specification, the EL (electroluminescence) spectrum refers to (1) a PL (photoluminescence) spectrum that reflects the unique characteristics of a light emitting material such as a dopant material or a host material included in the organic light emitting layer and , (2) is calculated as a product of an out-coupling emittance spectrum curve, which is determined according to the structure and optical properties of an organic light emitting device including the thickness of organic layers such as an electron transport layer.

1 is a cross-sectional view showing a white light emitting device according to a first embodiment of the present invention.

As shown in FIG. 1 , the white light emitting device according to the first embodiment of the present invention has a first electrode 110 and a second electrode 200 opposite to each other on a substrate 100 , and the first electrode 110 . ) and the second electrode 200 with the charge generating layer 150 interposed therebetween, a first stack S1 and a second stack S2 are provided.

The first stack S1 includes a first hole transport related common layer 1210 , a blue light emitting layer 130 , and a first electron transport related common layer 1220 on the first electrode 110 .

In addition, the second stack S2 is a second hole transport related common layer 1230, first to third light emitting layers 141, 142, 143 that are sequentially stacked and gradually emit short wavelengths, and a second electron transport related common layer ( 1240).

The first and second hole transport related common layers 1210 and 1230 are layers related to hole injection and hole transport, and may include at least one of a hole transport layer (HTL/HTL2, HTL3) and an electron blocking layer. have. In addition, the first hole transport-related common layer 1210 may further include a hole injection layer (HIL) 121 that is in contact with the first electrode 110 and lowers the interfacial resistance when holes are injected from the first electrode 110 . have. The first and second hole transport related common layers 1210 and 1230 may be formed of a single layer or a plurality of layers. As shown, in one stack, there may be multiple layers, and in the other stack, there may be a single layer. And, for example, when including a plurality of layers, such as the first hole transport related common layer 1210 of the first stack S1 of FIG. 1 , the hole transport layer HTL2 close to the light emitting layer 130 is the light emitting layer ( 130 ) may function as an electron blocking layer that prevents electrons or excitons from escaping from the hole transport layer 122 .

The first and second electron transport-related common layers 1220 and 1240 are layers related to electron transport and the rate at which electrons are supplied to adjacent light emitting layers, and among the electron transport layers ETL1 and ETL2 and the hole blocking layer It may include at least one. In addition, the second electron transport-related common layer 1240 may further include an electron injection layer that is in contact with the second electrode 200 and lowers interfacial resistance when electrons are injected from the second electrode 200 . The first and second electron transport related common layers 1220 and 1240 may be formed of a single layer or a plurality of layers.

In the white light emitting device according to the first embodiment of the present invention, the first stack S1 includes a single blue light emitting layer 130 to emit blue light. The blue color may have an emission peak at 430 nm to 490 nm.

Unlike the first stack S1 , the second stack S2 has a plurality of light emitting layers in contact with each other in the phosphorescent light emitting unit 140 , and each of the first to third light emitting layers 141 , 142 , 143 has a longer wavelength than blue. emit different light. In addition, the first to third emission layers 141 , 142 , and 143 emit red, yellow-green, and green wavelengths, respectively. That is, the first emission layer 141 emits light having an emission peak of 590 nm to 650 nm, the second emission layer 142 emits light having an emission peak of 540 nm to 590 nm, and the third emission layer 143 is Light having an emission peak of 510 nm to 560 nm is emitted. The light of the third light emitting layer 143 , which emits the shortest wavelength in the second stack S2 , has a longer wavelength than the light of the blue light emitting layer 130 .

The reason that the first to third light emitting layers 141 , 142 , and 143 different from each other are provided in the second stack S2 is to enrich the color to be expressed in the light emitting display device. The more the light emitting layers are included, the greater the color reproduction effect and the larger the color reproduction range obtainable from the light emitting display device. This means that the range overlapping with the DCI standard and the BT2020 standard is wide.

The long-wavelength emission layers of the second stack S2 may be implemented as a phosphorescent emission layer with high efficiency, and sequentially go to the third emission layer 143 , the second emission layer 142 , and the first emission layer 141 , and gradually drive the threshold voltage. Since this is lowered, energy not used for this in the upper light emitting layer in the second stack S2 can be used in the lower light emitting layer. Accordingly, efficiency in the second stack S2 may be increased. To make this possible, the long-wavelength emission layer is gradually applied to the third emission layer 143 , the second emission layer 142 , and the first emission layer 141 so that the driving threshold voltage is gradually lowered. In the example of FIG. 1 , an example in which the first light-emitting layer 141 is a red light-emitting layer, the second light-emitting layer 142 is a yellow-green light-emitting layer, and the third light-emitting layer 143 is a green light-emitting layer is used.

On the other hand, the white light emitting device of the present invention has a thickness difference in the light emitting layers 141 , 142 , and 143 in the second stack S2 in a structure in which the plurality of light emitting layers of the white light emitting device are adjacent to each other. That is, the thickness of the second light emitting layer 142 is the thickest among the light emitting layers of the second stack S2 , and the thickness of the third light emitting layer 143 is the thinnest. That is, the thickness relationship of the second light emitting layer 142 > the first light emitting layer 141 > the third light emitting layer 143 between the light emitting layers 140 that emit phosphorescence. Here, the second light emitting layer 142 expresses white color, which has the largest specific gravity, and may be the thickest in the second stack S2, and the first light emitting layer 141 and the third light emitting layer 143 are the second light emitting layer ( 142), the thickness is thin. The reason why the third light-emitting layer 143 is thinner than the first light-emitting layer 141 is that the third light-emitting layer 143, which is sensitive to thermal stress in the backside during the deposition process, is thinned in the substrate 100 generated at a low current density. This is to alleviate or prevent color anomalies in the edge region.

Meanwhile, in the white light emitting device of the present invention, the organic stack OS of the first stack S1 on the upper side of the first electrode 110 , the charge generation layer 150 and the second stack S2, and the second electrode ( 200 are layers continuously formed in the display area of the substrate 100 without distinction. That is, when there are a plurality of sub-pixels on the substrate 100 , the first electrode 110 is divided for each sub-pixel, but the upper components do not use a fine metal mask, and at least the display area It is formed integrally with respect to In this case, the white light emitting device of the present invention can omit the application of the fine metal mask after the formation of the first electrode 110 , thereby improving processability and improving yield reduction caused by the difference in alignment for each mask. There is this. In addition, in the white light emitting device of the present invention, white light is expressed by summing lights of different colors emitted by the plurality of stacks S1 and S2, and a color filter (109R. 109G and 109B), different colors may be emitted for each sub-pixel. Each layer of the organic stack OS of the white light emitting device of the present invention may be formed through an open mask with the entire display area of the substrate 100 open.

The layers of the first stack S1 , the charge generation layer 150 , the layers of the second stack S2 , and the second electrode 200 integrally formed with respect to the display area are formed of a material vaporized from a source in a deposition chamber. formed by supplying In this case, in the deposition process of each layer, a difference in thermal gradient may occur in the center region and the edge region even in the display region of the substrate 100 , and even the deposition surface of the same layer may have a difference in entropy.

In addition, the deposition temperature of the organic material is different for each layer. In particular, since the light emitting layers of the second stack are continuous, the substrate 100 continuously receives heat as it goes upward, and the third light emitting layer 143 is deposited last among the light emitting layers. During deposition, the difference in the thermal gradient for each region of the substrate 100 is deepened, so that the thickness difference between the central region and the edge region may be larger. In the example of FIG. 1 , by reducing the overall thickness of the third light-emitting layer 143 in the second stack S2 , the influence of the third light-emitting layer 143 on the difference in the thermal gradient for each area of the substrate 100 is reduced.

Specifically, the thickness relationship between the light emitting layers in the phosphorescent light emitting unit 140 will be described in detail in relation to the effect below.

The blue light emitting layer 130 and the first to third light emitting layers 141 , 142 , and 143 each include a host and a dopant. And, if necessary, the host may be provided in single or plural in each light emitting layer.

The blue emission layer 130 includes a fluorescent dopant, and the first to third emission layers 141 , 142 , and 143 relatively include a phosphorescent dopant with high efficiency. The phosphorescent dopant of the first to third light emitting layers 141 , 142 , and 143 is iridium (Ir), platinum (Pt), or osmium (Os). It is a metal complex compound containing gold (Au), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), palladium (Pd) or ttrium (Tm). The host of the first to third emission layers 141 , 142 , and 143 may include a host having an electron transport characteristic and/or a host having a hole transport characteristic. In addition, the phosphorescent dopants of the first to third emission layers 141 , 142 , and 143 have a difference in the triplet level T1 required for this.

On the other hand, the charge generation layer 150 located between the stacks S1 and S2 may include an n-type charge generation layer 151 and a p-type charge generation layer 153 as shown, or a single host. It may be formed as a single layer including an n-type dopant and a p-type dopant.

The first electrode 110 and the second electrode 200 function as an anode and a cathode, and the first electrode 110 includes a transparent electrode, and the second electrode 200 includes a reflective electrode. can

2 is a cross-sectional view illustrating a white light emitting device according to a second embodiment of the present invention.

As shown in FIG. 2 , the white light emitting device according to the second embodiment of the present invention has the lower and upper portions of the phosphor stack PS including the first to third light emitting layers 141 , 142 , and 143 as compared with the first embodiment. A first blue light emitting stack BS1 and a second blue light emitting stack BS2 that emit blue light respectively are provided in the . That is, the white light emitting device according to the second embodiment has a difference in that a plurality of blue light emitting stacks are provided in order to increase the efficiency of blue, which is relatively insufficient compared to the phosphorescent stack PS.

Charge generation layers 150 and 170 are provided between each stack. As shown, the charge generation layers 150 and 170 may include the n-type charge generation layers 151 and 171 and the p-type charge generation layers 153 and 173 in a stacked form, or a single host. It may be formed as a single layer including an n-type dopant and a p-type dopant.

Although the illustrated example shows a single sub-pixel, the first electrode 110 may be divided and patterned for each sub-pixel to correspond to a plurality of sub-pixels. In addition, the organic stack OS and the second electrode 200 on the first electrode 110 may be formed in a plurality of sub-pixels without distinction.

Even in the white light emitting device according to the second embodiment of the present invention, the first electrode 110 is divided for each sub-pixel, but the upper components do not use a fine metal mask and are integrated with respect to at least the display area. will be formed with In this case, the white light emitting device of the present invention can omit the application of the fine metal mask after the formation of the first electrode 110 , thereby improving processability and improving yield reduction caused by the difference in alignment for each mask. There is this. In addition, in the white light emitting device of the present invention, white light is expressed by summing lights of different colors emitted by the plurality of stacks S1 and S2, and a color filter (109R. 109G and 109B), different colors may be emitted for each sub-pixel.

The first blue light emitting stack BS1 includes a first hole transport related common layer 1210 , a first blue light emitting layer BEML1 130 , and a first electron transport related common layer 124 on the first electrode 110 . this is provided

In addition, the second stack S2 includes a second hole transport related common layer 125, first to third light emitting layers 141, 142, 143 that are sequentially stacked and gradually emit short wavelengths, and a second electron transport related common layer ( 126).

In addition, the second blue light emitting stack BS2 includes a third hole transport related common layer 1250 , a second blue light emitting layer BEML2 160 , and a third electron transport related common layer 129 .

The third hole transport-related common layer 1250 may include a plurality of hole transport layers 127 and 128, similar to the first blue light emitting stack BS1, of which the hole transport layer (HTL5) 128 is located on the upper side. may function as an electron blocking layer.

In addition, the first electrode 110 may include a transparent electrode, and the second electrode 200 may include a reflective electrode, so that light generated from the organic stack OS may be emitted through the first electrode 110 . .

On the other hand, the second electrode 200 may be formed of a plurality of layers, and a layer in contact with the organic stack OS among the plurality of layers is composed of an inorganic compound including a metal and a halogen material such as fluorine to function as an electron injection layer. may be When the electron injection layer is made of an inorganic material or an inorganic compound, it may be formed in a chamber different from that of the organic stack OS, and may be formed in the same mask and/or in the same chamber as the second electrode 200 .

The first and second embodiments each include a phosphorescent stack S2 or PS having a phosphorescent unit 140 in which a plurality of phosphorescent light-emitting layers are sequentially stacked, and briefly review the principle of light emission of the phosphorescent stack PS. see.

3 is a view showing a second stack of a white light emitting device of the present invention.

As shown in FIG. 3 , holes are supplied to the phosphorescence unit 140 from the second hole transport related common layer 125 in the second stack S2 , and electrons from the second electron transport related common layer 126 are transferred to the phosphorescent unit ( 140), excitons are generated by recombination of holes and electrons in each of the first to third light emitting layers 141, 142, and 143, and light emission occurs when the energy of the excitons falls to the ground state.

The first to third light emitting layers 141 , 142 , and 143 serve as a second electron transport related common layer 126 between the second hole transport related common layer 125 and the second electron transport related common layer 126 . It gradually emits light of a shorter wavelength, and goes to the second light emitting layer 142 , the first light emitting layer 141 and the third light emitting layer 143 , and has a thin thickness.

Here, the thickness of the second light emitting layer 142 is the thickest among the light emitting layers of the second stack S2 , and the thickness of the third light emitting layer 143 is the thinnest. That is, the thickness relationship of the second light emitting layer 142 > the first light emitting layer 141 > the third light emitting layer 143 between the light emitting layers 140 that emit phosphorescence. Here, the second light emitting layer 142 expresses white color, which has the largest specific gravity, and may be the thickest in the second stack S2, and the first light emitting layer 141 and the third light emitting layer 143 are the second light emitting layer ( 142), the thickness is thin. The reason why the third light-emitting layer 143 is thinner than the first light-emitting layer 141 is that the third light-emitting layer 143, which is sensitive to thermal stress in the backside during the deposition process, is thinned in the substrate 100 generated at a low current density. This is to alleviate or prevent color anomalies in the edge region.

The total thickness of the phosphorescent light emitting unit 140 including the first to third light emitting layers 141 , 142 , and 143 may be 350 Å to 450 Å. Since there are a total of three light emitting layers in the phosphorescent light emitting unit 140 , the first to third light emitting layers 141 , 142 , and 143 are distributed to the total thickness of the phosphorescent light emitting unit 140 . The phosphorescent light emitting unit 140 has light emitting layers that can be implemented with a high-efficiency phosphorescent light emitting material in the order of wavelength, where the first light emitting layer 141 emits red light, and the second light emitting layer 142 emits yellow-green light. Light is emitted, and the third light-emitting layer 143 emits green light.

The thinnest thickness of the third light emitting layer 143 may be 20% to 30% of the total thickness of the phosphorescent light emitting unit 140 . The thickness of the third light-emitting layer 143 may be thinner than that of the first light-emitting layer or the second light-emitting layer.

The reason that the thickness of the third light emitting layer 143 in the white light emitting device of the present invention is the thinnest is that the third light emitting layer 143 emitting green light has a color coordinate change due to the current density. This is because it is larger than the second light emitting layers 141 and 142 .

Hereinafter, changes in color coordinates of experimental examples according to changes in current density will be described. Hereinafter, the color coordinate change is mainly observed at a low current density (0.25 mA/cm ² ~10 mA/cm ² ), which can be visually observed as a large change in color coordinates is particularly significant at a low current density.

4A to 4D are graphs showing the relationship between current density and CIEy color coordinates of Experimental Examples 1 to 4;

(141/142/143 thickness ratio) Ex1
(0.75:1:1) Ex2
(0.75:1:0.55) Ex3
(0.75:1:0.5) Ex4
(0.75:1:0.45) ΔCIEx at low current 0.019 0.016 0.016 0.017 ΔCIEy at low current 0.048 0.045 0.043 0.037 Frame G level (at 32Gray judged) 4 4 2 One Absence of color you you radish radish

The first to fourth experimental examples (Ex1, Ex2, Ex3, Ex4) have a structure of the white light emitting device having the structure of FIG. 2 in common, and the thickness ratio of the first to third light emitting layers 141 , 142 , and 143 , respectively was changed to Specifically, in the first to fourth experimental examples (Ex1, Ex2, Ex3, Ex4), in common, the second light-emitting layer 142 is the thickest, and the first light-emitting layer 141 based on the thickness of the second light-emitting layer 142 . was set to 0.75 times the thickness of the second light emitting layer 142 . The first to fourth experimental examples (Ex1, Ex2, Ex3, and Ex4) have a difference in the thickness of the third light-emitting layer 143 , and are 1 times, 0.55 times, 0.5 times, and 0.45 times the thickness of the second light-emitting layer 142 , respectively. When the white color is implemented with a low current density, the CIEx color coordinate change (ΔCIEx), the CIEy color coordinate change (ΔCIEy), and the edge G level value are judged, and the presence or absence of color abnormality is determined. In the first to fourth experimental examples (Ex1, Ex2, Ex3, Ex4), the change in CIEx color coordinates (ΔCIEx) was all less than 0.020, and the change was small. On the other hand, in the first to fourth experimental examples (Ex1, Ex2, Ex3, Ex4), the CIEy color coordinate change (ΔCIEy) is larger than each CIEx change, and in particular, in the first and second experimental examples (Ex1, Ex2), the CIEy The color coordinate change is a large difference between the change in the high current density (more than 10 mA/cm ² ) and the change in the low current density (0.25 mA/cm ² to 10 mA/cm ² ), as shown in FIGS. 4A and 4B , CIEy There is a phenomenon in which green color is observed more strongly, unlike white expression of high current density, when driven at a low current density with a large change. However, it can be seen that the change in CIEy (ΔCIEy ) in the second experimental example (Ex2) is relatively smaller when the low current density and high current density are driven compared to the first experimental example (Ex1).

In addition, through Table 1, from the first experimental example (Ex1) to the fourth experimental example (Ex4), as the thickness of the third light emitting layer 143 is reduced, the change in CIEy (ΔCIEy) at low current density becomes smaller. In addition, it can be seen that the tendency of CIEy change at low current density and high current density is also similar.

The frame G level in Table 1 is judged at 32 gray, and a larger number means a deviation from the normal range. And, the presence or absence of color abnormality is judged through the CIEy color coordinate change (ΔCIEy) and the edge gray level value. means

Through the above experiment, color abnormalities occurred when driving at low current density in the first experimental example (Ex1) and the second experimental example (Ex2), whereas in the third experimental example (Ex3) and the fourth experimental example (Ex4) It can be confirmed that the color abnormality defect has been resolved.

In addition, when comparing the first experimental example (Ex1) and the second experimental example (Ex2), it can be seen that the change in CIEy (ΔCIEy) gradually decreases, through which the phosphorescent light emitting unit ( 140), when comparing the thickness of the second light emitting layer 142 and the third light emitting layer 143, the thickness of the third light emitting layer 143 can be expected to be effective in 45% or more and less than 55% of the thickness of the second light emitting layer 142. .

Hereinafter, by fixing the relationship between the second and third light-emitting layers and changing the thickness of the first light-emitting layer, the presence or absence of color abnormalities during low current density driving and the tendency to change in current density are examined.

5A and 5B are graphs showing the relationship between current density and CIEy color coordinates in Experimental Examples 4 and 5;

(141/142/143 thickness ratio) Ex4 (0.75:1:0.45) Ex5 (0.65:1:0.45) ΔCIEx at low current 0.017 0.018 ΔCIEy at low current 0.037 0.039 Frame G level (at 32Gray judged) One One Absence of color radish radish

As shown in Table 2, the thickness of the third light-emitting layer was fixed to 0.45 times the thickness of the second light-emitting layer, and the low current density (0.25 mA/cm ² to 10 mA) in the fourth and fifth experimental examples (Ex4, Ex5). /cm ² ), when measuring the CIEy change value (ΔCIEy), it is 0.037 and 0.039 in Experimental Example 4 and Experiment 5, respectively, and gray levels are all 1 in the edge region of the display area of the substrate, the fourth and fifth It can be confirmed that no color abnormality occurs in all of the experimental examples. That is, in this case, when the thickness of the first light emitting layer is 0.65 to 0.75 times that of the second light emitting layer, the color abnormality occurs when driving at low current density. It can be confirmed that this does not occur.

)내지 34.1%(

)의 두께로 할 수 있다. Through the above experimental results, the first light emitting layer 143 with respect to the total thickness of the first to third light emitting layers is 29.5% (

) to 34.1% (

) in thickness.

On the other hand, the third light emitting layer 143 is set to 20% to 30% of the total thickness of the first to third light emitting layers. The relatively large range of the thickness of the third light emitting layer 143 is for the following reason.

6 is a plan view illustrating a light emitting display device according to the present invention, and FIG. 7 is a view illustrating a change in the thickness of the third light emitting layer along line I to I' of FIG. 6 .

In the light emitting display device of the present invention, as shown in FIG. 6 , a display area AA in which a substrate 100 includes a plurality of sub-pixels SP, a pad part PAD around the display area AA, and the display area It may include a non-display area NA in which link wires connecting the wires AA and the pad part PAD, and a ground wire and power supply voltage wires are disposed.

In the light emitting display device of the present invention, each layer and the second electrode 140 of the organic stack OS of FIGS. 1 and 2 include the entire display area AA, and the non-display area of the display area AA (NA) It is formed by extending in part.

Each layer of the organic stack OS of the light emitting display device of the present invention may be formed through an open mask (not shown) in which the entire display area of the substrate 100 is opened.

In addition, the phosphorescent emission layers 140 ( 141 , 142 , and 143 ) of the second stack S2 and PS of the organic stack OS are also formed to extend to the entire display area AA and a part of the non-display area NA. . This is because the open area 140 of the open mask (not shown) has the shape of the open area 140 by providing additional margins in all directions by completely covering the display area AA in consideration of the margin when the open mask is aligned.

However, the substrate 100 in the deposition chamber has different thermal gradient characteristics in the central region and the edge region due to a difference in a region where the heat source is located, and exhibits a relatively lower temperature tendency in the edge region than in the center. There is a difference in entropy on the deposition surface of (100). A side having a lower entropy tends to be thickly stacked in a relatively stable state. In the edge region, the entropy is relatively lower than in the central region, and accordingly, the organic layer may be thickly stacked in the edge region than in the center.

In particular, when the organic material layer is formed before the formation of the third light emitting layer 143, which is the lowest among the optically functioning phosphorescent light emitting layers in the second stack, a thermal difference for each area applied is weighted, and as shown in FIG. 7 , the display area NA ), a difference in thickness occurs between the edge region and the center region, and the tendency appears as a phenomenon in which the edge region accumulates thicker. There is a difference in entropy of the deposition surface for each region, and since the third emission layer is relatively thickly stacked on the edge region, for example, when the phosphorescent emission layer is formed to have the same thickness, the thickness deviation between the central region and the edge region of the third emission layer becomes severe. , which results in different color change tendencies in the edge region and the center region.

That is, in the light emitting display device of the present invention, the color inversion abnormality is eliminated when driving the low current density between the colors of the first to third light emitting layers in the phosphorescent light emitting unit 140 , and the third light emitting layer is relatively rearward in the deposition order. In this case, the thickness of the third light emitting layer is lowered in the entire phosphorescent light emitting unit to minimize the effect of the thickness difference of the third light emitting layer in consideration of the difference in thickness between the edge region and the center region.

In this case, referring to FIG. 7 , the thickness of the third emission layer in the center region has a difference of 8.3% or less compared to the thickness of the third emission layer in the edge region in the display region.

Meanwhile, although the third emission layer 143 is further formed in a portion of the non-display area NA, the thickness of the third emission layer 143 accumulated in the non-display area NA does not affect the display.

In the light emitting display device of the present invention, even when deposition is performed without changing the number of masks or the shape of the masks, by varying the thickness ratio of the first to third light emitting layers, it is possible to solve the color abnormality in the edge (edge region). have.

Hereinafter, the light emitting display device of the present invention will be described in relation to the above-described light emitting device emitting white light, as well as a thin film transistor and a color filter.

8 is a cross-sectional view illustrating a light emitting display device according to the present invention, and FIG. 9 is a circuit diagram of a sub-pixel according to an example of the light emitting display device according to the present invention.

As shown in FIG. 8 , in the light emitting display device 1000 of the present invention, at least one blue light emitting stack S1 or BS1/ as shown in FIG. 1 or 2 , between the first electrode 110 and the second electrode 200 . BS2) and an organic stack OS including a phosphorescent light emitting stack S2 or PS in which a plurality of phosphorescent light emitting layers are stacked. Between the blue light emitting stack and the phosphorescent light emitting stack is a charge generating layer. In addition, a hole transport-related common layer and an electron transport-related common layer are included in the lower and upper portions of the blue light-emitting layer (B EML or B EML1/B EML2) of the blue light-emitting stack (S1 or BS1/BS2), respectively, and in the phosphorescent light-emitting stack The phosphorescent light emitting unit 140 of the first to third light emitting layers 141, 142, and 143 that gradually emits a short wavelength is provided, and the lower and upper portions of the phosphorescent light emitting unit 140 have a hole transport related common layer and an electron transport related layer, respectively. A common layer is included.

Each sub-pixel emits white light through the organic stack 200 in the first electrode 110 and the second electrode 200, and includes color filters 109a, 109b, and 109c on the light output side. It's a different color for each.

In the illustrated example, the thin film transistor array is provided on the side from which the light is emitted, and the light emitted through the first electrode 110 passes through the substrate 100 through the color filters 109a, 109b, and 109c.

The display device of the present invention includes a substrate 100 having a plurality of sub-pixels R_SP, G_SP, B_SP, and W_SP, and the white light emitting device ( OLED), a thin film transistor (TFT) provided in each of the sub-pixels and connected to the first electrode 110 of the above-described white organic light emitting diode (OLED), and the first electrode of at least one of the sub-pixels The color filter layers 109R, 109G, and 109B provided on the lower side of 110 may be included.

Although the illustrated example describes an example including the white sub-pixel W_SP, the present invention is not limited thereto, and the white sub-pixel W_SP is omitted and only the red, green, and blue sub-pixels R_SP, G_SP, and B_SP are provided. will also be possible In some cases, a combination of a cyan sub-pixel, a magenta sub-pixel, and a yellow sub-pixel capable of expressing white by replacing the red, green, and blue sub-pixels may be combined.

The thin film transistor TFT includes, for example, a gate electrode 102 , a semiconductor layer 104 , and a source electrode 106a and a drain electrode 106b connected to both sides of the semiconductor layer 104 .

A gate insulating layer 103 is provided between the gate electrode 102 and the semiconductor layer 104 .

The semiconductor layer 104 may be formed of, for example, amorphous silicon, polycrystalline silicon, an oxide semiconductor, or a combination of two or more of these. For example, when the semiconductor layer 104 is an oxide semiconductor, a channel protective layer 105 may be further provided in direct contact with the semiconductor layer 104 to prevent damage to the channel portion of the semiconductor layer 104 . can

In addition, the drain electrode 106b of the thin film transistor TFT may be connected to the first electrode 110 and the contact hole CT region provided in the first and second passivation layers 107 and 108 .

The first passivation layer 107 is provided to primarily protect the thin film transistor TFT, and color filters 109R, 109G, and 109B may be provided thereon.

When the plurality of sub-pixels SP includes a red sub-pixel R_SP, a green sub-pixel G_SP, a blue sub-pixel B_SP, and a white sub-pixel W_SP, the color filter layer is a white sub-pixel W_SP ), the first to third color filters 109R, 109G, and 109B are provided in the remaining sub-pixels, and the white light emitted through the first electrode 110 passes through each wavelength. A second passivation layer 108 is formed under the first electrode 110 to cover the first to third color filters 109R, 109G, and 109B. The first electrode 110 is formed on the surface of the second passivation layer 108 except for the contact hole CT.

Here, the white light emitting device OLED includes an organic stack OS between the transparent first electrode 110 and the second electrode 200 of the reflective electrode opposite to the first electrode 110 to provide light through the first electrode 110 . to eject

Reference numeral 119, which is not described herein, denotes a bank, and BH between banks denotes a bank hole. Light is emitted to an area opened through the bank hole, and the bank hole defines a light emitting part of each sub-pixel.

The display device of FIG. 8 shows, for example, a display device according to a bottom emission method. However, the display device of the present invention is not limited to this example, and in the structure of the display device of FIG. 8 , the color filter layer is positioned above the second electrode 200 , the first electrode 110 includes a reflective metal, and , the second electrode 200 may be implemented as a top emission method by forming a transparent electrode or a semi-transmissive metal.

Alternatively, the color filter layer may be omitted or provided, and a transparent organic light emitting device may be implemented by using both the first and second electrodes 110 and 120 as transparent electrodes.

Each of the sub-pixels SP may include a white light emitting device OLED, a driving transistor DT, a plurality of switching transistors, and a capacitor Cst as shown in FIG. 9 . The plurality of switching transistors may include first and second switching transistors ST1 and ST2. 9, for convenience of explanation, a j-th (j is an integer greater than or equal to 2) data line Dj, a q-th reference voltage line Rq (where q is an integer greater than or equal to 2), and k-th (k is an integer greater than or equal to 2) Only the pixel P connected to the gate line Gk and the kth initialization line SEk is illustrated.

The white light emitting device OLED emits light according to a current supplied through the driving transistor DT. A first electrode of the white light emitting diode OLED may be connected to a source electrode of the driving transistor DT, and a second electrode may be connected to a first power voltage line VSSL to which a first power voltage is supplied. The first power voltage line VSSL may be a low potential voltage line to which a low potential power voltage is supplied.

The driving transistor DT is disposed between the second power voltage line VDDL to which the second power voltage is supplied and the organic light emitting diode OLED. The driving transistor DT adjusts a current flowing from the second power voltage line VDDL to the organic light emitting diode OLED according to a voltage difference between the gate electrode and the source electrode. The gate electrode of the driving transistor DT is connected to the first electrode of the first switching transistor ST1 , the source electrode is connected to the second power voltage line VDDL, and the drain electrode is connected to the second electrode of the organic light emitting diode (OLED). It can be connected to one electrode. The second power voltage line VDDL may be a high potential voltage line to which a high potential power voltage is supplied.

The first switching transistor ST1 is turned on by the k-th gate signal of the k-th gate line Gk to supply the voltage of the j-th data line Dj to the gate electrode of the driving transistor DT. The gate electrode of the first switching transistor ST1 is connected to the k-th gate line Gk, the source electrode is connected to the gate electrode of the driving transistor DT, and the drain electrode is connected to the j-th data line Dj. can

The second switching transistor ST2 is turned on by the k-th initialization signal of the k-th initialization line SEk to connect the q-th reference voltage line Rq to the drain electrode of the driving transistor DT. The gate electrode of the second switching transistor ST2 is connected to the k-th initialization line SEk, the first electrode is connected to the q-th reference voltage line Rq, and the second electrode is the drain electrode of the driving transistor DT. can be connected to

The capacitor Cst is formed between the gate electrode and the source electrode of the driving transistor DT. The capacitor Cst stores a difference voltage between the gate voltage and the source voltage of the driving transistor DT.

One electrode of the capacitor Cst is connected to the gate electrode of the driving transistor DT and the source electrode of the first switching transistor ST1, and the other electrode of the capacitor Cst is the source electrode of the driving transistor DT and the second switching transistor. It may be connected to the drain electrode of ST2 and the first electrode of the organic light emitting diode OLED.

The driving transistor DT, the first switching transistor ST1, and the second switching transistor ST2 of each of the sub-pixels P may be formed of a thin film transistor. In addition, in FIG. 3 , the driving transistor DT, the first switching transistor ST1, and the second switching transistor ST2 of each of the pixels P are formed of an N-type semiconductor transistor having an N-type semiconductor characteristic. , the embodiments of the present specification are not limited thereto. That is, the driving transistor DT, the first switching transistor ST1 , and the second switching transistor ST2 of each of the pixels P may be formed of a P-type semiconductor transistor having a P-type semiconductor characteristic.

The white light emitting device of the present invention described above can increase the diversity of color expression by providing different red light emitting layers, yellow green light emitting layers and green light emitting layers in the phosphorescent light emitting stack. Therefore, it is possible to increase the efficiency without color change.

In the light emitting display device having a white light emitting device of the present invention, the thickness of the green light emitting layer is the thinnest among the light emitting layers of different colors stacked on each other in the phosphorescent light emitting stack, so that the thickness of the green light emitting layer is the total thickness of the phosphorescent light emitting layer in the phosphorescent light emitting stack. By lowering it, it is possible to reduce the sensitivity to color abnormalities caused by the green light emitting layer for each area. Accordingly, it is possible to prevent a color abnormality from appearing in the edge area within the display area.

In addition, in the light emitting display device of the present invention, the color coordinate variation during low current driving and high current driving in the edge region and the center region in the display region of the substrate by setting the thickness ratio of the red light emitting layer and the green light emitting layer to a constant ratio compared to the yellow and green light emitting layer to be similar, color abnormality can be prevented when driving at low current density.

To this end, in a light emitting display device according to an embodiment of the present invention, a first electrode and a second electrode facing each other on a substrate, and between the first electrode and the second electrode, a first light emitting device is provided. a stack and a second stack including the first stack and a second stack having first to third light emitting layers stacked therebetween with a first charge generating layer therebetween, wherein the first to third light emitting layers are disposed away from the first stack The shorter wavelength light is gradually emitted, and the thickness of the third light-emitting layer may be thinner than that of the first light-emitting layer or the second light-emitting layer.

In addition, the thickness may be thin while going to the second light emitting layer, the first light emitting layer, and the third light emitting layer.

Each of the first to third light-emitting layers may be a phosphorescent light-emitting layer.

The first light emitting layer emits a second light having an emission peak of 590 nm to 650 nm, the second light emitting layer emits a third light having an emission peak of 540 nm to 590 nm, and the third light emitting layer has an emission peak of 510 nm to 560 nm. A fourth light may be emitted, and the fourth light may have a longer wavelength than the first light.

The first light may have an emission peak of 430 nm to 490 nm, and the first stack may include a fourth emission layer emitting the first light.

A third stack including a second charge generation layer and a fifth emission layer emitting the first light may be further included on the second stack.

A color filter layer and a thin film transistor connected to the first electrode may be further included between the substrate and the first electrode.

The first emission layer may be a red emission layer, the second emission layer may be a yellow-green emission layer, and the third emission layer may be a green emission layer.

The thickness of the first light-emitting layer may have a thickness of 65% to 75% with respect to the thickness of the second light-emitting layer, and the thickness of the third light-emitting layer may have a thickness of 45% to 55% with respect to the thickness of the second light-emitting layer have.

Further, in a light emitting display device according to another embodiment of the present invention, a substrate having a plurality of sub-pixels, a first electrode provided in each sub-pixel on the substrate, and the plurality of sub-pixels facing the first electrode a second electrode provided across the pixels, between the first electrode and the second electrode, across the plurality of sub-pixels, a first stack emitting a first light, the first stack, and a charge generation layer; and a second stack having first to third light-emitting layers stacked therebetween, wherein the first to third light-emitting layers gradually emit light of a shorter wavelength as the distance from the first stack increases, the second light-emitting layer; The thickness of the first light emitting layer and the third light emitting layer may be thin.

A total thickness of the first to third emission layers may be 350 Å to 450 Å, and a thickness of the third emission layer may be 20% to 30% of a total thickness of the first to third emission layers.

The thickness of the third emission layer may be greater in the sub-pixels located in the edge region of the substrate than in the sub-pixels located in the central region of the substrate.

On the other hand, the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications and changes can be made within the scope without departing from the technical spirit of the present invention. It will be clear to those of ordinary skill in the art.

110: first electrode 1210: first hole transport related common layer
121: hole injection layer 122: first hole transport layer
123: second hole transport layer 124: first electron transport related common layer
125: second hole transport related common layer 126: second electron transport related common layer
127: third hole transport layer 128: fourth hole transport layer
129: third electron transport related common layer PS: phosphorescent stack
130: first blue light emitting layer 140: phosphorescent light emitting unit
141: first light-emitting layer 142: second light-emitting layer
143: third light emitting layer 150, 170: charge generation layer
160: second blue light emitting layer 200: second electrode
1210: first hole transport related common layer 1250: third hole transport related common layer
BS1, BS2: Blue Stack OS: Organic Stack

Claims (19)

a first electrode and a second electrode facing each other on the substrate;
Between the first electrode and the second electrode, a first stack emitting a first light and a second stack having the first stack and first to third light-emitting layers stacked with a first charge generating layer interposed therebetween including,
The first to third light-emitting layers gradually emit light of a shorter wavelength as the distance from the first stack increases,
A thickness of the third light emitting layer is thinner than a thickness of the first light emitting layer or the second light emitting layer. The method of claim 1,
Each of the first to third light-emitting layers is a phosphorescent light-emitting layer,
The total thickness of the first to third light emitting layers is 350Å to 450Å,
The thickness of the third light emitting layer is 20% to 30% of the total thickness of the first to third light emitting layers. 3. The method according to claim 1 or 2,
A thickness of the third light emitting layer is thicker in an edge region of the substrate than in a central region of the substrate. 3. The method of claim 2,
A thickness of the first light emitting layer is 29.5% to 34.1% of a total thickness of the first to third light emitting layers. The method of claim 1,
The first light emitting layer emits a second light having an emission peak of 590 nm to 650 nm,
The second light emitting layer emits a third light having an emission peak of 540 nm to 590 nm,
The third light emitting layer emits a fourth light having an emission peak of 510 nm to 560 nm,
The fourth light has a longer wavelength than the first light. The method of claim 1,
The first light has an emission peak of 430 nm to 490 nm,
The first stack is a white light emitting device including a fourth light emitting layer for emitting the first light. The method of claim 1,
The white light emitting device further comprising: on the second stack, a third stack including a second charge generating layer and a fifth light emitting layer emitting the first light. The method of claim 1,
The thickness of the first light-emitting layer has a thickness of 65% to 75% of the thickness of the second light-emitting layer,
The thickness of the third light emitting layer is a white light emitting device having a thickness of 45% to 55% of the thickness of the second light emitting layer. The method of claim 1,
The first light-emitting layer is a red light-emitting layer, the second light-emitting layer is a yellow-green light-emitting layer, and the third light-emitting layer is a green light-emitting layer,
The thickness of the first light-emitting layer has a thickness of 65% to 75% of the thickness of the second light-emitting layer,
The thickness of the third light emitting layer is a white light emitting device having a thickness of 45% to 55% of the thickness of the second light emitting layer. a substrate having a plurality of sub-pixels;
a first electrode provided in each sub-pixel on the substrate;
a second electrode provided across the plurality of sub-pixels to face the first electrode;
A first stack emitting a first light, a first stack emitting a first light between the first electrode and the second electrode, across the plurality of sub-pixels, and first to first stacked layers with a charge generation layer interposed therebetween a second stack having 3 light-emitting layers;
The first to third light-emitting layers gradually emit light of a shorter wavelength as the distance from the first stack increases,
A thickness of the third emission layer is thinner than a thickness of the first emission layer or the second emission layer. 11. The method of claim 10,
Each of the first to third light-emitting layers is a phosphorescent light-emitting layer,
The total thickness of the first to third light emitting layers is 350Å to 450Å,
A thickness of the third light emitting layer is 20% to 30% of a total thickness of the first to third light emitting layers. 12. The method of claim 10 or 11,
The thickness of the third emission layer is thicker in the sub-pixels located in the edge region of the substrate than in the sub-pixels located in the center region of the substrate. 12. The method of claim 11,
The thickness of the first light emitting layer is 29.5% to 34.1% of the total thickness of the first to third light emitting layers. 11. The method of claim 10,
The first light emitting layer emits a second light having an emission peak of 590 nm to 650 nm,
The second light emitting layer emits a third light having an emission peak of 540 nm to 590 nm,
The third light emitting layer emits a fourth light having an emission peak of 510 nm to 560 nm,
The fourth light has a longer wavelength than the first light. 11. The method of claim 10,
The first light has an emission peak of 430 nm to 490 nm,
and the first stack includes a fourth light emitting layer that emits the first light. 11. The method of claim 10,
The light emitting display device of claim 1, further comprising: a third stack on the second stack, the third stack including a second charge generating layer and a fifth light emitting layer emitting the first light. 11. The method of claim 10,
The light emitting display device further comprising: a color filter layer between the substrate and the first electrode; and a thin film transistor connected to the first electrode. 11. The method of claim 10,
The thickness of the first light-emitting layer has a thickness of 65% to 75% of the thickness of the second light-emitting layer,
A thickness of the third light emitting layer is 45% to 55% of a thickness of the second light emitting layer. 11. The method of claim 10,
The first light-emitting layer is a red light-emitting layer, the second light-emitting layer is a yellow-green light-emitting layer, and the third light-emitting layer is a green light-emitting layer,
The thickness of the first light-emitting layer has a thickness of 65% to 75% of the thickness of the second light-emitting layer,
A thickness of the third light emitting layer is 45% to 55% of a thickness of the second light emitting layer.

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